1. Field of the Invention
The invention relates to an oil pump drive control apparatus that supplies oil pressure to an automatic transmission of a motor vehicle or the like. More particularly, the invention relates to an oil pump drive control apparatus that supplies oil pressure to an automatic transmission of a hybrid vehicle, a vehicle that performs an idling stop, etc., by using a first oil pump driven cooperatively with the drive power source and a second oil pump independent of the drive power source.
2. Description of the Related Art
Recently, in order to reduce emission gas and improve fuel economy, there are provided hybrid vehicles, idling-stop type vehicles, etc. in which a drive power source (e.g., an engine, en electric motor, etc.) is automatically stopped when the vehicle is stopped (or when a predetermined condition is met). Such a vehicle has a mechanical oil pump that is mechanically connected to the drive power source in a cooperative fashion, and an electric oil pump that is electrically driven by a battery or the like independently of the drive power source, in order to supply oil pressure to a hydraulic control apparatus and a speed shift mechanism of an automatic transmission, etc. The vehicle is designed so that when the drive power source is stopped, the mechanical oil pump is stopped, and therefore, the electric oil pump 8, independent of the drive power source, is driven in order to supply a needed oil pressure to the automatic transmission.
An example of the apparatus for driving and controlling the aforementioned oil pumps is an oil pump drive control apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-170888. This apparatus detects a case where it is expected that the mechanical oil pump is not being driven based on a stopped state of the drive power source and the like. On the basis of the detection result, the apparatus supplies oil pressure by driving the electric oil pump, so as to maintain an oil pressure needed for the hydraulic control of the automatic transmission.
However, the oil pump drive control apparatus described in the aforementioned patent application performs a drive control of the electric oil pump based on the stopped state of the drive power source or the like. Therefore, the electric oil pump is driven before the mechanical oil pump stops. The electric oil pump is stopped after the mechanical oil pump is stopped. Therefore, the electric oil pump is driven while a sufficient oil pressure from the mechanical oil pump remains, and the electric oil pump is stopped after the oil pressure from the mechanical oil pump has risen to a sufficiently high level. Hence, there is a problem of increase in the operation load on the electric oil pump. Furthermore, the increased operation load causes increased electric power consumption and reduced amount of charge stored in the battery. Therefore, the operation time of the electric oil pump is reduced and the durability thereof may suffer. Still further, if an electric oil pump is provided so as to withstand the aforementioned load, there arises a problem of an increased size of the electric oil pump.
Contrary to the aforementioned patent application, there is a method in which the electric oil pump is driven after the mechanical oil pump is stopped, and the electric oil pump is stopped before the mechanical oil pump is driven. However, this method has a problem in that the oil pressure needed for the hydraulic control apparatus cannot be maintained, and therefore a shock occurs at the time of restarting the drive power source.
Accordingly, it is an object of the invention to provide an oil pump drive control apparatus that solves the aforementioned problems by driving and controlling the second oil pump based on the oil pressure of the hydraulic control apparatus.